The present invention relates to a method of starting a multi-cylinder, direct-injection, internal combustion engine, in particular of a motor vehicle, without using a starter motor. The position of a piston in a cylinder of the internal combustion engine is determined and fuel is injected into a combustion chamber of the cylinder whose piston is in the working phase, and the fuel is ignited immediately thereafter. This triggers the starting operation.
The present invention also relates to a memory element, in particular a read-only memory, a random-access memory or a flash memory for a control unit of an internal combustion engine, in particular in a motor vehicle. A computer program which is capable of running on a computing element, in particular on a microprocessor, is stored in the memory element.
The present invention also relates to a computer program capable of running on a computing element, in particular a microprocessor.
The present invention also relates to a direct-injection, multi-cylinder, internal combustion engine, in particular in a motor vehicle. The internal combustion engine provides for determining the position of a piston in a cylinder of the internal combustion engine, a fuel metering system for injection of fuel into a combustion chamber of the cylinder whose piston is in a working phase, and an ignition arrangement for igniting the fuel injected into the cylinder immediately after injection. This triggers the starting operation.
Finally, the present invention relates to a control unit of a direct-injection, multi-cylinder, internal combustion engine, in particular in a motor vehicle. The internal combustion engine provides for determining the position of a piston in a cylinder of the internal combustion engine, a fuel metering system for injection of fuel into a combustion chamber of a cylinder and an ignition arrangement for igniting the fuel injected into the cylinder at a preselectable time. The control unit controls the determining of the position of a piston, the fuel metering system and the ignition means for triggering the starting operation, so that the fuel metering system injects fuel into a combustion chamber of the cylinder whose piston is in a working phase, and the ignition arrangement ignites the fuel injected into the cylinder immediately after injection.
German Published Patent Application No. 197 42 969 describes a method of starting a multi-cylinder, direct-injection, internal combustion engine in which the serial injection sequence of the internal combustion engine is canceled by a parallel connection of working cycles via a suitable valve control for a rapid torque buildup. To this end, the internal combustion engine has intake and exhaust valves that are freely operable, inasmuch as allowed by free travel of the valves.
During at least one revolution of the crankshaft of the internal combustion engine, the intake valves of the cylinders whose pistons are at top dead center at the same time are opened. After executing an intake stroke and compression stroke, the compressed fuel in the combustion chambers of these cylinders is ignited simultaneously. Thus, two cylinders go through the working phase at the same time. Following the working stroke, the combustion gases are ejected through the exhaust valves of the cylinders which are opened at the same time. In this method, however, the starting operation is not accomplished by combustion in the cylinders but instead by an electric starter motor which is provided separately. It executes an intake stroke and/or a compression stroke before the first ignition.
A method of starting an internal combustion engine of the type described above without using a starter motor is described in German Published Patent Application No. 100 20 104, for example. In the method described, no intake stroke or compression stroke is carried out before the first ignition, and instead the starting operation is triggered by the ignition alone. The advantage of such a direct start of the internal combustion engine is in particular that it is possible to eliminate an electric drive motor for the start or for execution of an intake stroke and/or a compression stroke before the first ignition. Due to the absence of a compression stroke before the first ignition, however, an effective mechanism for preparing a fuel/air mixture contained in the combustion chamber is omitted.
Therefore, there is a need to improve upon the processing of the mixture at the beginning of the starting operation in the case of direct start of a multi-cylinder, direct-injection, internal combustion engine without using a starter motor.
The present invention proposes that as the starting operation continues immediately after ignition of fuel in the cylinder which is in the working phase, fuel is injected into a combustion chamber of another cylinder where the piston is in an intake phase, and the injected fuel is ignited while still in the intake phase.
The method according to the present invention is suitable for starting a direct-injection internal combustion engine having at least two cylinders without using a starter motor. Prior to beginning the method, the position of the rotation angle crankshaft of the internal combustion engine, i.e., the position of the pistons in the cylinders of the internal combustion engine, is determined. In the case of an internal combustion engine having four or more cylinders, the piston of at least one cylinder will be in the working phase. If in the case of an internal combustion engine having fewer than four cylinders, no piston of a cylinder is in the working phase, the intake and exhaust valves of the cylinder which is in the intake phase are brought into a position corresponding to the working phase, i.e., the intake and exhaust valves are closed.
For free operation of the intake and exhaust valves, a camshaft-free control is provided, for example, with which each intake and exhaust valve may be controlled separately from the other valves and independently of the position of the camshaft. For camshaft-free control, the intake and/or exhaust valves are equipped with a regulating unit either individually or jointly for a plurality of valves. The regulating unit may be actuated hydraulically, piezoelectrically, electromagnetically or by some other method. A plurality of camshaft-free controls for intake and exhaust valves are described from related art and may be used in conjunction with the present invention.
As an alternative, the intake and exhaust valves may have, e.g., a variable camshaft control element on the intake side and a variable valve lift for free actuation. It is thus possible to adjust the intake camshaft so that the intake valves are opened briefly in the intake phase only at the beginning and are thus brought into a position corresponding to the working phase. In this way, earlier closing of the intake may be set on the intake side.
Fuel is injected into the combustion chamber of the cylinder which is in the working phase, and the fuel is ignited immediately thereafter, thus starting the initial rotary motion of the internal combustion engine which thus triggers the starting operation. As the starting operation continues, fuel is injected into the combustion chamber of another cylinder in which the piston is in an intake phase immediately after ignition of the fuel/air mixture in the cylinder which is in the working phase. To further accelerate the rotary motion of the internal combustion engine, fuel injected into the combustion chamber of the additional cylinder is ignited while still in the intake phase.
Injection of fuel into the combustion chamber of a cylinder in the intake phase before the second combustion has a positive effect on preparing the mixture for the second combustion. At the start of the intake phase of a cylinder, the injector of the cylinder is opened to allow air to be drawn into the combustion chamber of the cylinder. Due to the intake of air through the intake valve, swirls develop in the combustion chamber of the cylinder and persist for a short period of time even after the intake valve has been closed. Fuel to be injected into the combustion chamber before the second ignition is injected into the swirls, thus resulting in an especially homogeneous mixture of fuel and air in the combustion chamber. Thus, in homogeneous operation, fuel is injected before the second ignition. The intake valve of the cylinder in the intake phase may be closed immediately before, during or even just after the injection of fuel. The method according to the present invention may also be used with internal combustion engines having multiple intake and/or exhaust valves per cylinder. To carry out the method according to the present invention, it is sufficient if at least one of the intake or exhaust valves is operated accordingly.
After ignition of the fuel/air mixture, especially good combustion is made possible due to the homogeneous distribution of the fuel/air mixture in the combustion chamber of the additional cylinder, so that with the second combustion an especially high torque may be transmitted to the crankshaft of the internal combustion engine. It has been found that when starting an engine without using a starter motor, the function of the first combustion is mainly to start the initial rotary motion of the crankshaft. However, the second combustion in particular is crucial for the success or failure of starting the engine without a starter motor. In the method according to the present invention, this second combustion may be improved significantly, so that secure and reliable starting of an internal combustion engine without using a starter motor is made possible.
According to an embodiment of the present invention, it is proposed that an intake valve of the additional cylinder in the intake phase shall be kept open during the fuel injection and shall be closed only shortly before ignition of the fuel. In this way, the turbulence in the combustion chamber of the additional cylinder is maintained to the full extent even during the injection of fuel. This yields an especially homogeneous distribution of the fuel/air mixture in the combustion chamber and subsequently complete combustion.
According to a another embodiment of the present invention, it is proposed that as the starting operation continues, fuel shall be injected into the combustion chambers of cylinders in either an intake phase or a compression phase and that the fuel compressed in the combustion chambers shall be ignited. The fuel/air mixture is thus ignited toward the end of the compression phase, just before reaching or just after passing top dead center. In this way, a third combustion and additional combustions are achieved, continuing and completing the starting operation of the internal combustion engine which has been initiated by the second combustion. The prerequisite for injection of fuel during the compression phase is that the fuel in the fuel metering system of the internal combustion engine should be available at a sufficiently high pressure. A sufficiently high injection pressure may be generated by using a high-pressure pump operated electrically, for example, independently of the internal combustion engine.
The fuel mass to be injected into the combustion chamber of the cylinder in the working phase at the beginning of the starting operation may be metered to yield an excess of oxygen for the first combustion. Because of the parallelism of the working cycles at the beginning of the starting operation, the cylinder which was in the working phase at the beginning of the starting operation is switched directly to a compression phase. No charge cycle may take place before the compression phase. Because of the oxygen excess during the first combustion, oxygen is still present in the combustion chamber of the cylinder after the first combustion, and together with fuel injected during the compression phase, it forms an ignitable fuel/air mixture. The high oxygen excess for the first combustion may be achieved through a stratified charge, for example.
After a first rotary motion of the internal combustion engine, one exhaust valve may be opened first by ignition and combustion of the fuel injected into the combustion chamber of the cylinder in the working phase before reaching a bottom dead center (UT), and then the exhaust valve is closed and an intake valve is opened before reaching the bottom dead center (UT). In this way, it is possible for oxygen to flow in before the start of the next compression in the cylinder, thus resulting in a clear improvement in combustion of the fuel/air mixture.
According to another embodiment of the present invention, it is proposed that fuel shall be injected into the combustion chambers of the cylinders during the starting operation at a pressure generated by a booster pump of the internal combustion engine. The pressure generated by a booster pump designed as an electric fuel pump (EKP) is also known as rail pressure EKP. In the case of internal combustion engines having a high-pressure pump driven as a function of the internal combustion engine or driven by the camshaft, fuel may be injected at rail pressure EKP during a starting operation without using a starter motor.
As an alternative, according to another embodiment of the present invention, it is proposed that fuel shall be injected into the combustion chambers of the cylinders during the starting operation at an injection pressure generated by a high-pressure pump of the internal combustion engine. Fuel may thus also be injected into the combustion chamber of the cylinder with no problem during the compression phase of the internal combustion engine. The injection pressure is generated by a high-pressure pump driven independently of the internal combustion engine, e.g., electrically.
Another embodiment of the method according to the present invention is in the form of a memory element which is provided for a control unit of an internal combustion engine, in particular in a motor vehicle. A computer program capable of running on a computing element, in particular on a microprocessor, and suitable for execution of the method according to the present invention is stored in the memory element. In this case, the present invention is thus implemented by a computer program stored on the memory element, so that this memory element provided with the computer program likewise represents the present invention as well as the method for whose execution the program is suitable. In particular an electric memory medium may be used as the memory element, e.g., a read-only memory, a random-access memory or a flash memory.
The present invention also relates to a computer program suitable for carrying out the method according to the present invention when it is run on a computing element, in particular a microprocessor. The computer program may be stored in a memory element, in particular a flash memory.
It is proposed on the basis of a direct-injection, multi-cylinder, internal combustion engine that immediately after ignition of the fuel in the cylinder in the working phase, as the starting operation continues, the fuel metering system injects fuel into a combustion chamber of another cylinder where the piston is in an intake phase, and the ignition arrangement ignites the injected fuel while still in the intake phase.
According to another embodiment of the present invention, it is proposed that the internal combustion engine shall provide for executing the method according to the present invention.
As yet another embodiment to achieve the object of the present invention, starting from a control unit of a direct-injection, multi-cylinder, internal combustion engine, it is proposed that immediately after ignition of the fuel in the cylinder in the working phase, the control unit shall control the determining of the position of a piston, the fuel metering system and the ignition means as the starting operation continues, the fuel metering system shall inject fuel into a combustion chamber of another cylinder which has a piston in an intake phase, and the ignition arrangement shall ignite the injected fuel while still in the intake phase.
According to another embodiment of the present invention, it is proposed that the control unit shall provide for executing the method according to the present invention.